| Volumes and Issues Contents of Issue 3 |
www.ocean-sci.net/6/621/2010/
doi:10.5194/os-6-621-2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
Seismic imaging of a thermohaline staircase in the western tropical North Atlantic
1Geophysical Institute, University of Bergen, Allégaten 70, 5007, Bergen, Norway
2BP America, Inc., 501 Westlake Park Blvd, Houston, TX 77079, USA
3Dept. of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, USA
4Dept. of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
5BP Exploration, Bldg H, Chertsey Road, Sunbury-on-Thames, TW16 7LN, UK
Abstract. Multichannel seismic data acquired in the Lesser Antilles in the western tropical North Atlantic indicate that the seismic reflection method has imaged an oceanic thermohaline staircase. Synthetic acoustic modeling using measured density and sound speed profiles corroborates inferences from the seismic data. In a small portion of the seismic image, laterally coherent, uniform layers are present at depths ranging from 550–700 m and have a separation of ~20 m, with thicknesses increasing with depth. The reflection coefficient, a measure of the acoustic impedance contrasts across these reflective interfaces, is one order of magnitude greater than background noise. Hydrography sampled in previous surveys suggests that the layers are a permanent feature of the region. Spectral analysis of layer horizons in the thermohaline staircase indicates that internal wave activity is anomalously low, suggesting weak internal wave-induced turbulence. Results from two independent measurements, the application of a finescale parameterization to observed high-resolution velocity profiles and direct measurements of turbulent dissipation rate, confirm these low levels of turbulence. The lack of internal wave-induced turbulence may allow for the maintenance of the staircase or may be due to suppression by the double-diffusive convection within the staircase. Our observations show the potential for seismic oceanography to contribute to an improved understanding of occurrence rates and the geographical distribution of thermohaline staircases, and should thereby improve estimates of vertical mixing rates ascribable to salt fingering in the global ocean.
Final Revised Paper (PDF, 1981 KB) Discussion Paper (OSD)
Citation: Fer, I., Nandi, P., Holbrook, W. S., Schmitt, R. W., and Páramo, P.: Seismic imaging of a thermohaline staircase in the western tropical North Atlantic, Ocean Sci., 6, 621-631, doi:10.5194/os-6-621-2010, 2010. Bibtex EndNote Reference Manager XML
